Effect of temperature, light length and water condition on Euphorbia hirta germination and seedling growth

To examine germination characteristics of the common weed Euphorbia hirta in tropical farmland and forest land, we studied the effects of temperature, light and water conditions on germination and seedling growth of E. hirta using petri-dish and pot-culture methods. The results showed that E. hirta seeds germinated between 20~40 ℃; the optimum germination temperature was 30 ℃, where germination rate and germination index were the highest. The optimum temperature for seedling growth was 25 ℃, where the root∶shoot ratio was 1.03∶1. Under constant temperature (25 ℃), there was no significant difference among seed germination rates with light length of 8-24 h (the average value was 94.07%); germination rate was reduced to 52% at 0 h/24 h (light/dark, L/D). The germination index first increased and then declined with shortened light length, with a maximal value of 93.93 at 16 h/8 h (L/D) and minimal value of 30.59 at 0 h/24 h (L/D). Seedling root lengths were markedly longer than shoot lengths with light and the opposite without light (P＜0.05). Under fluctuating temperature conditions (L/D:35 ℃/25 ℃), seed germination rate and seedling shoot length had no significant change (P＞0.05), but germination index and seedling root length were significantly decreased with shortened light length (P＜0.05). We concluded that light length of 12-16 h was the optimum light condition. Optimum seed germination and seedling growth of E. hirta occurred when soil moisture was 60% of the maximum water-holding capacity at 25 ℃ with 12 h/12 h (L/D), where emergence rate and root:shoot ratio were 39.38% and 1.10∶1, respectively.